Work vehicle
The work vehicle's controller system addresses the challenge of smooth direction switching and automatic brake activation by controlling brake operations based on vehicle speed and accelerator use, ensuring efficient and safe travel in various conditions.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-02-20
- Publication Date
- 2026-03-12
Smart Images
Figure JP2025005890_12032026_PF_FP_ABST
Abstract
Description
Work vehicles
[0001] The present invention relates to a work vehicle equipped with an automatic brake.
[0002] Conventionally, there has been known a technology relating to an automatic brake in a wheeled work vehicle that applies the brakes when predetermined operating conditions are met, regardless of whether the brake pedal is depressed or not (see, for example, Patent Documents 1 and 2).
[0003] Patent Documents 1 and 2 list the conditions for automatic braking to be activated as vehicle speed being less than a threshold value and the accelerator not being operated.
[0004] International Publication No. 2014 / 182879 Patent No. 5390615
[0005] Some work vehicles are known to be equipped with an FNR switch for switching forward and backward travel directions in addition to an automatic brake. It is desirable for such work vehicles to be able to switch forward and backward travel directions using the FNR switch even while traveling on flat ground, thereby ensuring work efficiency. In this case, the forward and backward travel directions are switched using the FNR switch while the accelerator pedal remains depressed. Therefore, when switching forward and backward travel directions using the FNR switch while traveling on flat ground, it is desirable to be able to smoothly switch forward and backward travel directions so that the vehicle can decelerate while the accelerator pedal remains depressed and accelerate in the opposite direction from the original travel direction. In this case, if the automatic brake is activated when switching travel directions, the forward and backward travel directions cannot be smoothly switched.
[0006] On the other hand, when the vehicle is on an uphill slope where it would move downwards if the accelerator pedal is not depressed, the vehicle may be stopped with the accelerator pedal depressed. In this case, it is desirable to activate the automatic brakes when the vehicle speed falls below a threshold.
[0007] However, if the conditions disclosed in Patent Documents 1 and 2 are applied as automatic brake activation conditions to a work vehicle equipped with an FNR switch in addition to an automatic brake, the operation of the automatic brake will change depending on how the accelerator is operated, so it is not possible to activate the automatic brake when switching between forward and backward travel on flat ground and when going uphill.
[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a work vehicle that can appropriately operate an automatic brake.
[0009] In order to achieve the above object, the present invention provides a work vehicle comprising a vehicle body capable of travelling, an accelerator that increases or decreases the vehicle body's speed depending on the amount of operation, a brake that brakes the vehicle body, a vehicle speed sensor that detects the vehicle body's speed, and a controller that controls the operation of the brake, and further comprising a direction switching device that switches the vehicle body's direction of travel, wherein when the direction switching device switches the vehicle body's direction of travel and the vehicle speed detected by the vehicle speed sensor becomes less than a threshold speed, if the amount of operation of the accelerator is equal to or greater than a predetermined amount, the controller does not activate the brake, and the direction switching device does not switch the vehicle body's direction of travel, but if the vehicle speed detected by the vehicle speed sensor becomes less than the threshold speed, the controller activates the brake regardless of the amount of operation of the accelerator.
[0010] According to the present invention, it is possible to obtain a work vehicle that can appropriately operate the automatic brake. Note that problems, configurations, and effects other than those described above will become apparent from the following description of the embodiment.
[0011] Fig. 1 is a side view of a wheel excavator; Fig. 2 is a diagram showing the inside of a cab; Fig. 3 is a circuit diagram of a hydraulic circuit of the wheel excavator; Fig. 4 is a hardware configuration diagram of the wheel excavator; Fig. 5 is a flowchart of a switching count process; Fig. 6 is a flowchart of an automatic brake activation process; and Fig. 7 is a flowchart of an automatic brake release process.
[0012] An embodiment of a work vehicle according to the present invention will be described with reference to the drawings. Fig. 1 is a side view of a wheel excavator 1, which is a representative example of a work vehicle according to this embodiment. In this specification, unless otherwise specified, front, rear, left, and right refer to the perspective of an operator who is riding on and operating the wheel excavator 1, and the side of the front work implement 10 from a cab 20 (described below) is considered the front side. Furthermore, specific examples of wheeled work vehicles are not limited to the wheel excavator 1, and the present invention can also be applied to wheeled work vehicles (for example, a wheel loader).
[0013] The wheel excavator 1 includes a lower traveling body 2 and an upper rotating body 3 rotatably supported on the lower traveling body 2. The lower traveling body 2 and the upper rotating body 3 are an example of a travellable vehicle body.
[0014] The lower traveling body 2 is equipped with a pair of left and right front tires 4F and a pair of left and right rear tires 4R. The steering angle of the front tires 4F is changed by operating a steering wheel 22, which will be described later. The front tires 4F and rear tires 4R (hereinafter, these may be collectively referred to as "tires 4") are rotated by the driving force of a traveling motor 38, which will be described later. This causes the lower traveling body 2 to travel.
[0015] The upper rotating body 3 is rotatably supported on the lower traveling body 2 via a swing bearing (not shown). The driving force of a swing motor (not shown) is transmitted to the upper rotating body 3, causing it to swing relative to the lower traveling body 2. The upper rotating body 3 includes a swing frame 5 serving as a base, a counterweight 6 disposed at the rear of the swing frame 5, a front working implement 10 supported at the center of the front end of the swing frame 5 and extending toward the front of the upper rotating body 3, and a cab (operator's seat) 20 disposed on the front left side of the swing frame 5.
[0016] The front working implement 10 includes a boom 11 supported on the upper rotating body 3 so that it can be raised and lowered, an arm 12 rotatably supported at the tip of the boom 11, a bucket 13 (attachment) rotatably supported at the tip of the arm 12, a boom cylinder 14 that drives the boom 11, an arm cylinder 15 that drives the arm 12, and a bucket cylinder 16 that drives the bucket 13. Note that specific examples of the attachment are not limited to the bucket 13, and may include a grapple, cutter, crusher, breaker, etc. The counterweight 6 is a heavy object that balances the weight of the front working implement 10.
[0017] Fig. 2 is a view showing the interior of the cab 20. The cab 20 has an interior space in which an operator who operates the wheel excavator 1 sits. As shown in Fig. 2, the interior of the cab 20 contains a seat 21 on which the operator sits and operation devices (22 to 29) that are operated by the operator seated in the seat. When the operator sitting in the cab 20 operates the operation devices (22 to 29), the lower traveling structure 2 travels, turns, and brakes, the upper rotating structure 3 rotates, and the front working implement 10 operates.
[0018] The operating devices (22 to 29) mainly include a steering wheel 22, an accelerator 23, a brake pedal 24, an FNR switch 25, an automatic brake switch 26, a gear change switch 27, left and right operating levers 28L, 28R, and a shutoff lever 29. However, specific examples of the operating devices are not limited to the above examples.
[0019] The steering wheel 22 is an operating device that changes the steering angle of the front tires 4F through operation by the operator. The accelerator 23 is an example of a speed operating device that increases or decreases the vehicle speed of the wheel excavator 1 (in other words, the rotation speed of the travel motor 38) depending on the amount of operation by the operator. The brake pedal 24 is an example of a braking operating device that brakes the wheel excavator 1 (in other words, activates brakes 44, 45, described below) depending on the amount of operation by the operator.
[0020] The FNR switch 25 is an example of a direction switching device that switches the traveling direction (forward, reverse, neutral) of the wheel excavator 1 through operation by the operator. More specifically, the FNR switch 25 is configured to be switchable among a forward position F that specifies the forward traveling direction of the wheel excavator 1, a reverse position R that specifies the reverse traveling direction of the wheel excavator 1, and a neutral position N that does not generate driving force regardless of the depression amount of the accelerator 23 (more specifically, does not supply hydraulic oil to the traveling motor 38). The FNR switch 25 then outputs a position signal indicative of the switched position to a controller 60 (described later). In other words, the forward position F and the reverse position R specify the traveling direction in which the wheel excavator 1 is capable of traveling. The neutral position N specifies a state in which the wheel excavator 1 is not capable of traveling.
[0021] The automatic brake switch 26 is an operating device that, when operated by an operator, switches whether or not to automatically activate the brakes 44, 45 (in other words, to cause the controller 60 to execute the processes of FIGS. 5 to 7 ). More specifically, the automatic brake switch 26 is configured to be switchable between an activated position ON, which automatically activates the brakes 44, 45, and a deactivated position OFF, which does not automatically activate the brakes 44, 45. When the automatic brake switch 26 is in the activated position ON, it outputs an automatic brake activation signal to the controller 60. The controller 60 receives the automatic brake activation signal and executes the processes of FIGS. 5 to 7 . When the automatic brake switch 26 is in the deactivated position OFF, it stops outputting the automatic brake activation signal.
[0022] The speed change switch 27 is an operating device that switches the gear ratio of a transmission 39 (described later) when operated by the operator. The speed change switch 27 outputs a speed change signal indicating the gear ratio to the controller 60. The control levers 28L, 28R are operating devices that are operated by the operator to operate the front working implement 10 (in other words, to extend and retract the boom cylinder 14, arm cylinder 15, and bucket cylinder 16). The shut-off lever 29 is an operating device that is operated by the operator to switch whether or not to operate the front working implement 10 in accordance with the operation of the control levers 28L, 28R. The shut-off lever 29 is configured to be switchable between an allowable position that allows operation of the front working implement 10 and a prohibitive position that prohibits operation of the front working implement 10. When the shut-off lever 29 is in the prohibitive position, it outputs a shut-off signal to the controller 60, and when it is in the allowable position, it stops outputting the shut-off signal.
[0023] [Configuration of Hydraulic Circuit 30] Fig. 3 is a circuit diagram of the hydraulic circuit 30 of the wheel excavator 1. As shown in Fig. 3, the wheel excavator 1 includes a hydraulic circuit 30. The hydraulic circuit 30 is a circuit for operating the wheel excavator 1. However, the specific configuration of the hydraulic circuit 30 is not limited to the example shown in Fig. 3 .
[0024] The hydraulic circuit 30 mainly includes an engine 31, a hydraulic oil tank 32, a main pump 33, a pilot pump 34, a traveling pilot pump 64, and a brake gear pump 65. The engine 31 is an example of a drive source that generates drive force to operate the wheel excavator 1. However, the drive source is not limited to the engine 31 and may be an electric motor. The main pump 33, the pilot pump 34, the traveling pilot pump 64, and the brake gear pump 65 are rotated by the drive force of the engine 31 and pump hydraulic oil stored in the hydraulic oil tank 32. The main pump 33 supplies hydraulic oil to hydraulic actuators (e.g., the boom cylinder 14, the arm cylinder 15, the bucket cylinder 16, and the traveling motor 38). The pilot pump 34 supplies pilot pressure oil to pilot ports of various valves (e.g., the brake valve 46 and the shutoff valve 48). The traveling pilot pump 64 supplies pilot pressure oil to the pilot port of the control valve 35. The brake gear pump 65 supplies hydraulic oil to the brakes 44 and 45 .
[0025] Furthermore, the hydraulic circuit 30 is a circuit for propelling the wheel excavator 1 and mainly comprises a control valve 35, a center joint 36, a counterbalance valve 37, a travel motor 38, a transmission 39, a gear ratio change valve 40, a travel pilot valve 41, a forward / reverse change valve 42, and a slow return valve 43.
[0026] The control valve 35 controls the amount and direction of hydraulic oil supplied from the main pump 33 to the travel motor 38 (in other words, the rotational speed and rotational direction of the travel motor 38) in accordance with the operator's operation of the accelerator 23 and FNR switch 25 (in other words, the supply direction of pilot pressure oil supplied to the pilot port and the travel operating pressure Pa).The hydraulic oil that passes through the control valve 35 is then supplied to the travel motor 38 via the center joint 36 and counterbalance valve 37.
[0027] The transmission 39 changes the speed of the rotational driving force of the travel motor 38 and transmits it to the tires 4. The gear ratio change valve 40 switches the supply direction of pilot pressure oil supplied from the pilot pump 34 to the transmission 39 in accordance with the control of the controller 60 (in other words, the gear change signal output from the gear change switch 27). This changes the gear ratio of the transmission 39 (for example, High, Low).
[0028] The travel pilot valve 41 adjusts the pressure (travel operating pressure Pa) of the pilot pressure oil supplied from the travel pilot pump 64 to the pilot port of the control valve 35 in accordance with the depression amount of the accelerator 23. More specifically, the travel pilot valve 41 increases the travel operating pressure Pa as the depression amount of the accelerator 23 increases, and decreases the travel operating pressure Pa as the depression amount of the accelerator 23 decreases.
[0029] The forward / reverse switching valve 42 switches the supply direction of pilot pressure oil from the traveling pilot pump 64 to the pilot port of the control valve 35 in accordance with the control of the controller 60 (in other words, the position signal output from the FNR switch 25). The slow return valve 43 delays the pilot pressure oil being discharged from the pilot port of the control valve 35 to the hydraulic oil tank 32. This allows the control valve 35 to gradually switch the supply direction of hydraulic oil to the traveling motor 38 (i.e., the traveling direction of the wheel excavator 1).
[0030] As a result, when the FNR switch 25 is switched from the forward position F to the reverse position R while the accelerator 23 is still depressed, the forward speed of the wheel excavator 1 gradually decreases until the vehicle speed V reaches zero, and then the reverse speed of the wheel excavator 1 gradually increases. Similarly, when the FNR switch 25 is switched from the reverse position R to the forward position F while the accelerator 23 is still depressed, the reverse speed of the wheel excavator 1 gradually decreases until the vehicle speed V reaches zero, and then the forward speed of the wheel excavator 1 gradually increases.
[0031] Furthermore, the hydraulic circuit 30 mainly includes brakes 44, 45, a brake valve 46, and an automatic brake valve 47 as a circuit for braking the wheel excavator 1. The brakes 44, 45 are an example of a braking device that brakes the wheel excavator 1 (more specifically, the tires 4) in accordance with the operator's operation of the brake pedal 24. More specifically, the brakes 44, 45 are hydraulic brakes that brake the wheel excavator 1 (more specifically, the rotation of the tires 4) by using hydraulic oil supplied from a brake gear pump 65.
[0032] The brake valve 46 adjusts the braking operation pressure Pb (braking force of the brakes 44, 45) of the hydraulic oil supplied from the brake gear pump 65 to the brakes 44, 45 in accordance with the depression amount of the brake pedal 24. More specifically, the brake valve 46 increases the braking operation pressure Pb (i.e., increases the braking force) as the depression amount of the brake pedal 24 increases, and decreases the braking operation pressure Pb (i.e., decreases the braking force) as the depression amount of the brake pedal 24 decreases.
[0033] Furthermore, the brake valve 46 adjusts the braking operation pressure Pb of the hydraulic oil supplied from the brake gear pump 65 to the brakes 44, 45 in accordance with the pilot pressure oil supplied to the pilot port through the automatic brake valve 47. The automatic brake valve 47 supplies pilot pressure oil from the pilot pump 34 to the pilot port of the brake valve 46 in accordance with the control of the controller 60 that has executed the processes shown in Figures 5 to 7.
[0034] The hydraulic circuit 30 also includes a shutoff valve 48 and front pilot valves 49L, 49R as circuits for operating the front work implement 10. The shutoff valve 48 switches between supplying pilot pressure oil supplied from the pilot pump 34 to the front pilot valves 49L, 49R or returning the pilot pressure oil to the hydraulic oil tank 32 in accordance with control by the controller 60 (more specifically, a shutoff signal output from the shutoff lever 29). The front pilot valves 49L, 49R control the pressure of the pilot pressure oil supplied from the pilot pump 34 to a pilot port of a front control valve (not shown) in accordance with operation of the control levers 28L, 28R by the operator. The front control valve controls the flow rate and supply direction of hydraulic oil from the main pump 33 to the front work implement 10 in accordance with this pilot pressure oil. This causes the front work implement 10 to operate.
[0035] The hydraulic circuit 30 further includes a travel operation pressure sensor 50 and a braking operation pressure sensor 51. The travel operation pressure sensor 50 detects the travel operation pressure Pa supplied to the pilot port of the control valve 35, and outputs a travel operation pressure signal indicating the detected travel operation pressure Pa to the controller 60. The braking operation pressure sensor 51 detects the braking operation pressure Pb supplied to the brakes 44, 45, and outputs a braking operation pressure signal indicating the detected braking operation pressure Pb to the controller 60.
[0036] That is, the traveling operation pressure Pa corresponds to the depression amount (operation amount) of the accelerator 23, and the braking operation pressure Pb corresponds to the depression amount (operation amount) of the brake pedal 24 or the pilot pressure supplied to the pilot port of the brake valve 46. The higher the traveling operation pressure Pa, the greater the depression amount of the accelerator 23, and the lower the traveling operation pressure Pa, the less the depression amount of the accelerator 23. Furthermore, the higher the braking operation pressure Pb, the greater the depression amount of the brake pedal 24 (the higher the pilot pressure supplied to the pilot port of the brake valve 46), and the lower the braking operation pressure Pb, the less the depression amount of the brake pedal 24 (the lower the pilot pressure supplied to the pilot port of the brake valve 46). However, the methods for detecting the depression amounts of the accelerator 23 and brake pedal 24 and the pilot pressure of the brake valve 46 are not limited to the above-mentioned examples.
[0037] [Configuration of Controller 60] Fig. 4 is a hardware configuration diagram of the wheel excavator 1. The wheel excavator 1 includes a controller 60. The controller 60 includes a CPU (Central Processing Unit) 61, which is an example of a processor, and a memory 62. The memory 62 is configured, for example, by a ROM (Read Only Memory), a RAM (Random Access Memory), an HDD (Hard Disk Drive), or a combination of these. The controller 60 realizes the processing described below by having the CPU 61 read and execute program code stored in the ROM or the HDD. The RAM is used as a work area when the CPU 61 executes the program.
[0038] However, the specific configuration of the controller 60 is not limited to this, and may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array).
[0039] The controller 60 controls the overall operation of the wheel excavator 1. The controller 60 controls the engine 31, the gear ratio change valve 40, the forward / reverse changeover valve 42, the automatic brake valve 47, and the shut-off valve 48 based on various signals output from the FNR switch 25, the automatic brake switch 26, the speed change switch 27, the shut-off lever 29, the travel operation pressure sensor 50, the braking operation pressure sensor 51, and the vehicle speed sensor 52. The vehicle speed sensor 52 detects the vehicle speed V, which is the speed of the vehicle body of the wheel excavator 1, and outputs a vehicle speed signal indicating the detected vehicle speed V to the controller 60. The vehicle speed V is an absolute value of speed (a scalar quantity).
[0040] The controller 60 controls the forward / reverse selector valve 42 in accordance with the position signal output from the FNR switch 25, thereby controlling the control valve 35 so that hydraulic oil is supplied to the travel motor 38 in a direction corresponding to the position of the FNR switch 25. The controller 60 executes the processes shown in Figures 5 to 7 while the automatic brake activation signal is being output from the automatic brake switch 26, and stops executing the processes shown in Figures 5 to 7 while the output of the automatic brake activation signal is stopped. The controller 60 also executes the processes shown in Figures 5 to 7 based on signals output from at least one of the FNR switch 25, the travel operation pressure sensor 50, the brake operation pressure sensor 51, and the vehicle speed sensor 52.
[0041] The controller 60 controls the gear ratio of the transmission 39 by controlling the gear ratio change valve 40 in accordance with the gear shift signal output from the gear change switch 27. The controller 60 controls the shutoff valve 48 to prohibit operation of the front working implement 10 while the shutoff signal is being output from the shutoff lever 29, and to allow operation of the front working implement 10 while the shutoff signal is not being output.
[0042] [Processing of Controller 60] When an automatic brake activation signal is output from the automatic brake switch 26, the controller 60 has a function of activating (automatically braking) the brakes 44, 45 if the activation conditions (S21 to S26) shown in FIG. 6 are satisfied, and releasing the automatic brakes if the release conditions (S31 to S36) shown in FIG. 7 are satisfied.
[0043] First, when the brake pedal 24 is depressed and the brakes 44, 45 are actuated (manual brakes) to stop the wheel excavator 1, it is desirable to activate the automatic brake. Also, on an uphill slope, the excavator may be stopped (balanced) simply by adjusting the accelerator 23 without depressing the brake pedal 24. In this case, it is desirable to activate the automatic brake once the wheel excavator 1 has stopped, even if the accelerator 23 is depressed. On the other hand, when the FNR switch 25 is switched with the accelerator 23 depressed, it is desirable to smoothly switch between forward and reverse travel without activating the automatic brake.
[0044] Therefore, the controller 60 controls the operation of the brakes 44, 45 based on the operation of the accelerator 23 and the FNR switch 25 and the vehicle speed V of the wheel excavator 1. More specifically, the controller 60 controls the activation and deactivation of the brakes 44, 45 based on the travel operation pressure signal (travel operation pressure Pa) output from the travel operation pressure sensor 50, the position signal (position of the FNR switch 25) output from the FNR switch 25, and the vehicle speed V detected by the vehicle speed sensor 52.
[0045] 5 is a flowchart of the switching count process. The switching count process is a process for counting the number of times (switching count n) that the FNR switch 25 is switched between the forward position F and the reverse position R while the wheel excavator 1 is decelerating. The controller 60 repeatedly executes the switching count process at predetermined time intervals while the wheel excavator 1 is traveling (in other words, when the vehicle speed V>0). The switching count n is stored in the memory 62.
[0046] When the FNR switch 25 is switched from either the forward position F or the reverse position R to the other (S11: Yes), the controller 60 adds 1 to the number of switchings n (S12). On the other hand, when the FNR switch 25 is not switched from either the forward position F or the reverse position R to the other and acceleration or stoppage of the wheel excavator 1 (vehicle speed V=0) is detected based on the output value of the vehicle speed sensor 52 (S11: No & S13: Yes), the controller 60 resets the number of switchings n (=0) (S14). Furthermore, when the FNR switch 25 is not switched from either the forward position F or the reverse position R to the other and, for example, during deceleration, acceleration or stoppage of the wheel excavator 1 is not detected based on the output value of the vehicle speed sensor 52 (S11: No & S13: No), the controller 60 ends the flow while maintaining the number of switchings n.
[0047] Note that "the wheel excavator 1 is decelerating" refers to a period during which the vehicle speed V detected by the vehicle speed sensor 52 is monotonically decreasing. Also, "the wheel excavator 1 is decelerating" includes a period during which the forward speed is decreasing and a period during which the reverse speed is decreasing. Also, "the wheel excavator 1 is accelerating" refers to an increase in the vehicle speed V detected by the vehicle speed sensor 52. Furthermore, "the wheel excavator 1 is stopping" refers to the vehicle speed V detected by the vehicle speed sensor 52 becoming zero. Here, deceleration, acceleration, and stopping of the wheel excavator 1 are not limited to being caused by adjustment of the accelerator 23, but also include being caused by the inclination of the ground.
[0048] 6 is a flowchart of the automatic brake activation process. The automatic brake activation process is a process for activating the brakes 44, 45 when predetermined activation conditions (S21 to S24) are satisfied. The controller 60 repeatedly executes the automatic brake activation process at predetermined time intervals while the wheel excavator 1 is traveling (in other words, when the vehicle speed V>0), in parallel with the switching count process.
[0049] First, while the wheel excavator 1 is decelerating (S21: Yes), the controller 60 waits until the vehicle speed V detected by the vehicle speed sensor 52 becomes less than the threshold speed Vth (S22: No) before executing the processing from step S23 onwards. Note that the threshold speed Vth is set, for example, to a value at which the wheel excavator 1 can be evaluated as being substantially stopped (i.e., a value close to zero). Then, if the controller 60 starts accelerating before the vehicle speed V becomes less than the threshold speed Vth (S22: No & S21: No), the controller 60 ends the automatic brake activation processing without executing the processing from step S23 onwards.
[0050] Furthermore, at the timing when the vehicle speed V becomes less than the threshold speed Vth (S22: Yes), the controller 60 determines whether the number of switching times n counted in the switching number count process executed in parallel is an odd number or an even number (S23). That is, the controller 60 determines whether the number of times the FNR switch 25 was switched between the forward position F and the reverse position R from the time the wheel excavator 1 started to decelerate until the time the vehicle speed V became less than the threshold speed Vth (S21: Yes & S22: Yes) is an odd number or an even number.
[0051] When the number of switching times n is an odd number, it means that the traveling direction indicated by the FNR switch 25 is opposite to the traveling direction of the wheel excavator 1. On the other hand, when the number of switching times n is an even number, it means that the traveling direction indicated by the FNR switch 25 is the same as the traveling direction of the wheel excavator 1. It should be noted that the even number includes 0 (i.e., the FNR switch 25 is not switched).
[0052] Then, when the number of switching times n during deceleration of the vehicle speed V detected by the vehicle speed sensor 52 is an even number (S21: Yes & S23: Yes), the controller 60 controls (opens) the automatic brake valve 47 at the timing when the vehicle speed V detected by the vehicle speed sensor 52 becomes less than the threshold speed Vth (S22: Yes), and activates the brakes 44, 45 regardless of the amount of operation of the accelerator 23 (S25). Such a situation can be considered, for example, when the wheel excavator 1 is stopped by depressing the brake pedal 24, or when the wheel excavator 1 is stopped on an uphill slope by adjusting only the accelerator 23.
[0053] That is, if the number of switching times n is an even number, the controller 60 determines that the traveling direction of the wheel excavator 1 has not been switched by the FNR switch 25. Then, if the traveling direction of the wheel excavator 1 has not been switched by the FNR switch 25 and the vehicle speed V detected by the vehicle speed sensor 52 is less than the threshold speed Vth, the controller 60 executes the processing from step S25 onwards, regardless of the amount of operation of the accelerator 23.
[0054] The controller 60 continues to operate the brakes 44, 45 until a release condition, which will be described later, is satisfied. Furthermore, the controller 60 stores in the memory 62 the travel operating pressure Pa (i.e., the operation amount of the accelerator 23) and the position of the FNR switch 25 at the time when the brakes 44, 45 start to be operated (S26).
[0055] On the other hand, if the number of switching times n is an odd number (S23: No), the controller 60 compares the travel operating pressure Pa (i.e., the operation amount of the accelerator 23) detected by the travel operating pressure sensor 50 with a predetermined first operating pressure P1 (first operation amount) (S24). The first operating pressure P1 is set to a value corresponding to the operation amount of the accelerator 23 to the extent that the travel direction is changed and the wheel excavator 1 is about to continue traveling.
[0056] Then, if the number of switching times n during deceleration of the vehicle speed V detected by the vehicle speed sensor 52 is an odd number (S21: Yes & S23: No), and if the traveling operating pressure Pa is less than the first operating pressure P1 at the time when the vehicle speed V detected by the vehicle speed sensor 52 becomes less than the threshold speed Vth (S22: Yes & S24: No), the controller 60 executes the processing of steps S25 to S26 (i.e., activates the brakes 44, 45). Such a situation is considered to be, for example, when the operator switches the FNR switch 25 in the direction opposite to the original traveling direction but intends to temporarily stop the wheel excavator 1.
[0057] On the other hand, if the number of switching times n during deceleration of the vehicle speed V detected by the vehicle speed sensor 52 is an odd number (S21: Yes & S23: No), and if the traveling operating pressure Pa is equal to or greater than the first operating pressure P1 at the time when the vehicle speed V detected by the vehicle speed sensor 52 becomes less than the threshold speed Vth (S22: Yes & S24: Yes), the controller 60 will not execute the processing of steps S25 to S26. In such a situation, for example, it is considered that the operator intends to continue traveling of the wheel excavator 1 by switching the FNR switch 25 in the direction opposite to the original traveling direction.
[0058] That is, when the number of switching times n is an odd number, the controller 60 determines that the traveling direction of the wheel excavator 1 has been switched by the FNR switch 25. In other words, the controller 60 determines whether or not the traveling direction has been switched based on the number of times the FNR switch 25 has been operated to switch the traveling direction. Then, when the traveling direction of the wheel excavator 1 has been switched by the FNR switch 25 and the vehicle speed V detected by the vehicle speed sensor 52 has become less than the threshold speed Vth, the controller 60 executes the processing from step S25 onwards if the traveling operating pressure Pa is less than the first operating pressure P1, and does not execute the processing from step S25 onwards if the traveling operating pressure Pa is equal to or greater than the first operating pressure P1.
[0059] 7 is a flowchart of the automatic brake release process. The automatic brake release process is a process for releasing the operation of the brakes 44, 45 when predetermined release conditions (S31 to S36) are met. The controller 60 repeatedly executes the automatic brake release process at predetermined time intervals while the brakes 44, 45 continue to be operated in step S25 (i.e., while the automatic brake valve 47 is open).
[0060] First, the controller 60 determines the position of the FNR switch 25 indicated by the position signal (S31). If the controller 60 determines that the FNR switch 25 is in the neutral position N (S31: No), the controller 60 ends the automatic brake release process without executing the processes from step S32 onwards (i.e., without releasing the operation of the brakes 44, 45), regardless of the depression amount of the accelerator 23 (travel operation pressure Pa).
[0061] On the other hand, if the controller 60 determines that the FNR switch 25 is in the forward position F or the reverse position R (S31: Yes), the controller 60 compares the position of the FNR switch 25 at the time when the brakes 44, 45 started to be actuated (i.e., the position of the FNR switch 25 stored in the memory 62 in step S26) with the position of the FNR switch 25 (S32). The controller 60 also compares the travel operation pressure Pa detected by the travel operation pressure sensor 50 with various threshold values (P1, P2, P3, P4, P0+α) (S33 to S36). Note that the threshold values P1, P2, and P4 may be the same value or different values.
[0062] If the FNR switch 25 has not been switched since the brakes 44, 45 began to operate (S32: Yes), and the operation amount of the accelerator 23 (driving operating pressure Pa) becomes smaller than the third operation amount (third operating pressure P3) (S33: Yes), and then increases to or above the second operation amount (second operating pressure P2) (S34: Yes), the controller 60 controls (closes) the automatic brake valve 47 to deactivate the operation of the brakes 44, 45 (S37).
[0063] One possible situation of this kind is when the brake pedal 24 is depressed to stop the wheel excavator 1 without depressing the accelerator 23, the automatic brake is activated, and then the accelerator 23 is depressed. As another example, one possible situation of this kind is when the FNR switch 25 is switched while traveling and the wheel excavator 1 is stopped without depressing the accelerator 23, the automatic brake is activated, and then the accelerator 23 is depressed. Note that the third operation amount (third operation pressure P3) is set to a value that is smaller (lower) than the first operation amount (first operation pressure P1) and the second operation amount (second operation pressure P2).
[0064] Furthermore, if the FNR switch 25 has not been switched since the brakes 44, 45 began to operate (S32: Yes), and the operation amount of the accelerator 23 (traveling operation pressure Pa) has increased by a predetermined value α or more since the start of operation of the brake 44 (i.e., the traveling operation pressure P0 stored in step S26) (S33: No & S35: Yes), the controller 60 executes the process of step S37. The predetermined value α is set to an extremely small value.
[0065] As an example, such a situation may occur when the wheel excavator 1 is stopped on an uphill slope with the accelerator 23 depressed, the automatic brake is activated, and then the accelerator 23 is depressed again.
[0066] Furthermore, when the FNR switch 25 is switched from the start of operation of the brakes 44, 45 (S32: No), and the operation amount of the accelerator 23 (travel operating pressure Pa) increases to or above the fourth operation amount (fourth operating pressure P4) (S36: Yes), the controller 60 executes the processing of step S37. Such a situation may occur, for example, when the brake pedal 24 is depressed to stop the wheel excavator 1, the automatic brake is activated, the traveling direction is changed using the FNR switch 25, and the accelerator is depressed again.
[0067] On the other hand, if the aforementioned release conditions are not met (S32: Yes & S33: Yes & S34: No / S32: Yes & S33: No & S35: No / S32: No & S36: No), the controller 60 terminates the automatic brake release process without executing the processing of step S37 (i.e., releasing the operation of the brakes 44, 45).
[0068] [Operation and Effect of the Embodiment] According to the above embodiment, when the FNR switch 25 is switched while the wheel excavator 1 is decelerating, it is determined whether or not to activate the brakes 44, 45 based on the depression amount of the accelerator 23. This makes it possible to appropriately determine whether the operator in the cab 20 is attempting to stop the wheel excavator 1 or to change the traveling direction and continue traveling, and to activate the automatic brakes accordingly. In other words, forward / reverse switching by switching the FNR switch 25 can be performed smoothly, and the automatic brakes can be appropriately activated when the operator intends to stop the excavator.
[0069] Furthermore, according to the above embodiment, if the FNR switch 25 is not switched during deceleration of the wheel excavator 1, the automatic brake is activated regardless of the depression amount of the accelerator 23. This makes it possible to activate the automatic brake both when the wheel excavator 1 is stopped by depressing the brake pedal 24 and when the wheel excavator 1 is stopped on an uphill slope by simply adjusting the accelerator 23.
[0070] Furthermore, according to the above embodiment, the accuracy of determining the activation conditions in the automatic brake activation process is improved by resetting the number of switching times n when the wheel excavator 1 accelerates or stops with the FNR switch 25 switched. As a result, the timing at which the brakes 44, 45 are activated can be controlled more appropriately.
[0071] Typically, an odd number of switches n is when N=1 (i.e., the traveling direction of the wheel excavator 1 is reversed), and an even number of switches n is when N=0 (i.e., the FNR switch 25 has not been switched). On the other hand, when the number of switches n is an odd number of 3 or more or an even number of 2 or more, it is possible that the operator has corrected an erroneous operation of the FNR switch 25, for example. In this way, redundancy can be increased by taking into consideration the correction of erroneous operation.
[0072] Furthermore, according to the above embodiment, the timing of releasing the automatic brake can be appropriately controlled by adding the state of the FNR switch 25 (S31 to S32) to the release conditions in addition to the amount of operation of the accelerator 23 (S33 to S36).
[0073] As one example, the automatic brake can be released when the accelerator 23 is released and then depressed again. In this case, the automatic brake can be released appropriately after the automatic brake has been activated, particularly when parking on flat ground. As another example, the automatic brake can be released when the depression amount of the accelerator 23 increases from when the automatic brake was first started. In this case, the automatic brake can be released appropriately after the automatic brake has been activated, particularly when parking on an uphill slope. As yet another example, the automatic brake can be released when the FNR switch 25 is switched and the accelerator 23 is depressed after the automatic brake has started. In this case, the automatic brake can be released appropriately after the automatic brake has been activated after parking and the traveling direction has been changed. On the other hand, by not releasing the automatic brake when the FNR switch 25 is in the neutral position N, it is possible to prevent the wheel excavator 1 from unexpectedly starting off against the operator's intention.
[0074] 1: Wheel excavator 2: Undercarriage 3: Upper rotating body 4: Tires 4F: Front tires 4R: Rear tires 5: Swing frame 6: Counterweight 10: Front implement 11: Boom 12: Arm 13: Bucket 14: Boom cylinder 15: Arm cylinder 16: Bucket cylinder 20: Cab 21: Seat 22: Steering wheel 23: Accelerator 24: Brake pedal 25: FNR switch 26: Automatic brake switch 27: Speed change switch 28L, 28R: Control lever 29: Shut-off lever 30: Hydraulic circuit 31: Engine 32: Hydraulic oil tank 33: Main pump 34: Pilot pump 35: Control valve 36: Center joint 37: Counterbalance valve 38: Travel motor 39: Transmission 40: Gear ratio change valve 41: Travel pilot valve 42: Forward / reverse changeover valve 43: Slow return valve 44, 45: Brake 46: Brake valve 47: Automatic brake valve 48: Shut-off valve 49L, 49R: Front pilot valve 50: Travel operation pressure sensor 51: Brake operation pressure sensor 52: Vehicle speed sensor 60: Controller 61: CPU 62: Memory 64: Steering gear pump 65: Brake gear pump
Claims
1. A work vehicle comprising: a vehicle body capable of travel; an accelerator that increases or decreases the vehicle body's speed depending on the amount of operation; a brake that brakes the vehicle body; a vehicle speed sensor that detects the vehicle body's speed; and a controller that controls the operation of the brake; further comprising a direction switching device that switches the vehicle body's traveling direction; wherein the controller does not activate the brake if the amount of operation of the accelerator is equal to or greater than a predetermined amount when the direction switching device switches the vehicle body's traveling direction and the vehicle speed detected by the vehicle speed sensor becomes less than a threshold speed; and activates the brake regardless of the amount of operation of the accelerator when the direction switching device does not switch the vehicle body's traveling direction and the vehicle speed detected by the vehicle speed sensor becomes less than the threshold speed.
2. A work vehicle as described in claim 1, characterized in that the controller determines that the direction switching device has not switched the vehicle's traveling direction when acceleration or stopping of the vehicle is detected based on the output value of the vehicle speed sensor.
3. A work vehicle as described in claim 1, characterized in that the controller determines whether the vehicle body's traveling direction has been switched based on the number of times the direction switching device switches the vehicle body's traveling direction.
4. A work vehicle as claimed in claim 1, characterized in that the controller releases the brake when the accelerator is operated while the brake is activated.
5. A work vehicle as described in claim 1, wherein the controller releases the brake when the accelerator operation amount increases from the time when the brake was first applied while the brake is applied.
6. A work vehicle as described in claim 1, wherein the controller, while the brake is activated, releases the brake when the direction switching device is switched and the accelerator operation amount increases from the time the brake starts to be activated.
7. A work vehicle as described in claim 1, wherein the direction switching device switches between the traveling direction of the vehicle body when the vehicle body is in a state where it is capable of traveling and a state where the vehicle body is unable to travel, and the controller does not release the operation of the brake regardless of the amount of operation of the accelerator when the direction switching device has made it impossible for the vehicle body to travel while the brake is activated.